A growing number of online service providers (Amazon, Yahoo!, Google, Snapfish, Mozy.com, etc.) aim to profit by storing and maintaining lots of valuable client data. Example uses of this storage include online backup, email, photo sharing, and video hosting. Many of these storage providers offer a small amount of “teaser” storage for free, and charge for larger, upgraded versions of the service.
Studies of deployed, large-scale storage systems show that no storage provider is completely reliable; all have the potential to lose or corrupt client data. Today, a client that wants to rely on these services must make an uneducated choice. Clients have only negative newsworthy anecdotes on which to base their decision, and service popularity or “brand name” is not a positive indicator of reliability. To know if their data is safe, clients must either blindly trust the storage provider or retrieve the hosted data and verify its integrity. To verify integrity, clients must maintain signatures of the hosted data, a task that is difficult for typical clients, e.g. home users. Neither solution is satisfactory. Unfortunately, to date, there are no fair and explicit mechanisms for making storage providers accountable for data loss.